sclass SuffixTree {
  Node root;
  S fullText;

  sclass Node {
    Substring text;
    // we either have children or positions
    O childrenOrPositions; // Map or IntBuffer
    
    // key is first character or -1 for end of string
    Map<Int, Node> children() {
      if (childrenOrPositions cast Map) ret childrenOrPositions; null;
    }
    
    IntBuffer positions() {
      if (childrenOrPositions cast IntBuffer) ret childrenOrPositions; null;
    }

    *() {}
    *(Substring *text) {}
    
    void addPosition(int i) {
      if (children() != null) fail("illegal node conversion to positions");
      if (positions() == null) childrenOrPositions = new IntBuffer;
      positions().add(i);
    }
    
    void addChild(Node n) {
      if (positions() != null) fail("illegal node conversion to children");
      if (children() == null) childrenOrPositions = new Map;
      children().put(charToIntOrMinus1(n.text), n);
    }
    
    Node getChild(int c) {
      ret mapGet(children(), c);
    }
  }

  *() {}
  *(S *fullText) {
    root = new Node(Substring(fullText, 0, 0));
    for i over fullText:
      addSuffix(Substring(fullText, i), i);
  }

  void addSuffix(Substring s, int position) {
    Node node = root;
    
    while (!empty(s)) {
      int _n = lCommonPrefix_CharSequence(node.text, s);
      s = s.substring(_n);
      if (_n >= l(node.text)) { // node text exhausted
        Node n = node.getChild(charToIntOrMinus1(s));
        if (empty(s)) {
          if (n != null) node = n;
          node.addPosition(position);
          ret;
        } else {
          if (n == null) {
            n = new Node(s);
            n.addPosition(position);
            node.addChild(n);
            ret;
          } else
            node = n;
        }
      } else { // node text not exhausted
        // split node. first, move all the node's vitals to a new node nOld
        Node nOld = new Node(node.text.substring(_n));
        nOld.childrenOrPositions = node.childrenOrPositions;
        node.childrenOrPositions = null;
        node.text = node.text.substring(0, _n);
        node.addChild(nOld);

        // now add a new node
        Node nNew = new Node(s);
        nNew.addPosition(position);
        node.addChild(nNew);
        ret;
      }
    }
  }

  public L<Int> indicesOf(S pattern) {
    new IntBuffer out;
    getIndicesOf(out, root, pattern, 0);
    ret out.asVirtualList();
  }
  
  void getIndicesOf(IntBuffer out, Node node, S pattern, int iPattern) {
    int lPattern = l(pattern);
    while true {
      int n = lCommonPrefix_CharSequence(node.text, Substring(pattern, iPattern));
      iPattern += n;
      if (iPattern >= lPattern) break;
      if (n < l(node.text)) break;
      Node child = node.getChild(charAtAsIntOrMinus1(pattern, iPattern));
      if (child != null) node = child;
    }
    
    collectPositions(out, node);
  }
  
  L<Int> getPositions(Node node) {
    new IntBuffer out;
    collectPositions(out, node);
    ret out.asVirtualList();
  }
  
  void collectPositions(IntBuffer out, Node node) {
    if (node == null) ret;
    out.addAll(node.positions());
    fOr (Node n : values(node.children()))
      collectPositions(out, n);
  }
  
  void printMe() {
    printNode("", "", root);
  }
  
  void printNode(S indent, S pre, Node node) {
    print(indent + pre + quote(shorten(20, node.text)) + (empty(node.positions()) ? "" : " " + node.positions()));
    fOr (int c, Node n : node.children())
      printNode(indent + "  ", "[" + (c < 0 ? "end" : quote((char) c)) + "] ", n);
  }
}

Began life as a copy of #1029202